On Saturday, 19 March 2016 at 17:41:29 UTC, Lass Safin wrote:
On Saturday, 19 March 2016 at 17:40:27 UTC, Lass Safin wrote:
Why:
enum Base {
A,
B,
}
enum Derived : Base {
C, // Gives error, says it can't implicitly convert
expression to Base.
D = 1, // Same error
E = cast(Base)294, // Finally works. Can only be
cast(Derived) instead.
}
void func(Derived d) {}
func(Derived.E); // works.
func(Derived.A); // Gives error, says it can't call function
with Base.A.
func(cast(Derived)Derived.A); // Works.
So, what's the proper way of extending an enum?
Meant "Can also be cast(Derived) instead."
"enum B : A" doesn't mean "B extends A", but rather "enum B
containing members of type A". Not specifying a type makes it
implicitly convertible to int, I think.
If you're looking to extend a named enum, I think you have to
create a new one. It will become a new type too, though that
might not matter.
enum Foo { first=123, second=456, third=789 } // int type inferred
enum Bar : int { // the ": int" here is important
first = Foo.first, // implicit cast to int
second = Foo.second,
third = Foo.third,
fourth = 42,
fifth = 0
}
If you don't define Bar as having members of type int, it will
guess that you want Foo (because we're assigning members with
values of Foo's). They would be limited to the range of values
Foo offers, and Bar.fourth = 42 is irreconcilabe with that.
